Of course, you can implement these things yourself in Javascript, but why should you do that? Are you sure that copy-pasted code you found on the internet really works correctly on all browsers, or was it an 80% solution that got lots of upvotes on StackOverflow by people that didn't test it very thoroughly? Do you want to have to learn a hundred different browser gotchas the hard way, and is that really a good use of your time?

It is in place in a legacy app, but I have been trying to use more standard JavaScript. I came across this GitHub repo with some good examples to help in going from jQuery to standard JavaScript github.com/nefe/You-Dont-Need-jQuery

I would say legacy codebases. Mostly WordPress themes with jQuery libraries. I still enjoy using jQuery for quick fixes and getting stuff done easily. If it is already in a project, then I see no reason not to use it. Otherwise if I can I will use just vanilla and Vue.

jQuery is more than just a bunch of features. It is also an opinion on how to do things. For example if you want to hide an element in vanilla JS do you use visibility or display?

For someone who has used jQuery for a long time, pulling in an 80K library and calling $('elm').hide() just makes sense. If jQuery is still supported, they get the performance they need and behavior they expect why should they change it? Wouldn't it make more sense to spend their time focusing on delivering value to their users?

jQuery also has a rich ecosystem of plugins an extensions that would be a pain to reproduce if you decided to migrate everything to vanilla js. Again you have to decide what is the most valuable use of your time.

It is understandable why people get excited about new technology but sometimes we forget why we are doing it. I would be more likely to shift from jQuery to a framework for code organization and maintainability than I would to vanilla js just because I can. The users of your site don't care if you use $() or document.querySelector.

I use jQuery because it is a library that performs very well and helps me do things in a pragmatic way. No doubt that JavaScript has gotten better but there are things that can be done via jQuery which are more elegant and easier to maintain. You write and application once and maintain it forever. There is nothing wrong with jQuery in 2019 or beyond. Web developers use dozens of libraries to make their lives easier. jQuery is no different in this regard.

It's fine if you can or want to write applications without jQuery but don't expect a gold star just because you didn't.